Help please-Which type of metal bolt for heat exchanger end cap?

[Mike k]

Damn ......... trying to nip it up as I saw some crystals at the joint I have sheared the bolt that holds the circular end cap (and rubber seal) onto the raw water heat exchanger. It looks like a brass bolt but I cannot be sure of its exact type also we think its 3/16 unc and about 1/2 inch long.

To give you an idea the heat exchanger has two cylinders one on top of the other - the larger cylinder is the main heat exchanger and the smaller cylinder attached underneath I think is a fluid cooler. Its on a Mercruiser 4.2 D tronic engine.

The problem is the fluid cooler bolt ,I have put in a temporary bolt which I found lying around and I have no idea what type of metal it is , it could just be mild steel, but also it is not a good fit so its weeping and so need to sort this really quickly. Can anyone advise what METAL type the bolt should be to avoid any anode issues and then do you know anywhere that can supply very quickly. I have emailed Keypart but something tells me they wont have any in stock right now.

Any advice on the metal type and a possible suppler would be great.

Many thanks for any help with this

Mike

 

[spannerman]

Got the same cooler on my Mercruiser and the bolts aren't brass, I and they aren't rusty so they must be stainless.

 

[Mike k]

Got the same cooler on my Mercruiser and the bolts aren't brass, I and they aren't rusty so they must be stainless.

Thanks Spannerman but I have just cleaned them up on my bench and they do look brass coloured - any further view?

 

[superheat6k]

If they are decent quality stainless they will be non magnetic. I would use either phophor-bronze or stainless and coat thoroughly with waterproof grease (not copper slip)

 

[Beamishken]

They are usually stainless if there not they have been changed at some time. UNC sounds about right shouldn't be too difficult to source from a decent nut & bolt place

if your on a sterndrive I think its the same thread as the anode bolt at the front of the leg (im not 100%sure but well worth checking) you get new ones with an anode set so maybe a spare lying with your old anodes (or anyone else in the marina with an alpha or bravo leg)

 

[Hadenough]

They are bronze on mine.

 

[Beamishken]

IIRC they screw into a blind hole so no need to worry from an anode point of view as the water cant get into the bolt

 

[Mike k]

If they are decent quality stainless they will be non magnetic. I would use either phophor-bronze or stainless and coat thoroughly with waterproof grease (not copper slip)

thanks Superheat - would I assume A4 316 would be decent enough?

 

[Mike k]

IIRC they screw into a blind hole so no need to worry from an anode point of view as the water cant get into the bolt

Hi Ken

Thank for your posts , mines an inboard so unfortunately the anode idea of the leg wont work for me . I have a feeling that the nut sheared off because the water can get at the bolt just behind the head where it goes through a 2.5 mm neoprene washer which is between the end cap and the unit. Anyway I think Tom from Tompa Marine is going to kindly sort me out with the bolts.( Thanks Tom).

 

[burgundyben]

I'd go to the dealer and get the replacement, that'll ensure you get the correct material.

You want the correct strength and galvanic property too.

 

[aquapower]

I'd go to the dealer and get the replacement, that'll ensure you get the correct material.

You want the correct strength and galvanic property too.

That's exactly what I done with my Volvo.

If they prove difficult to source through dealer then look at the others and see if any of the numbers/letters are visible, this will help in identifying material.